stack canaries don't work with user mode threads

[andrewboie]

Enabling CONFIG_STACK_CANARIES breaks user mode threads. Entering any function will result in a memory protection error, for example on x86:

***** CPU Page Fault (error code 0x00000004)
User thread read address 0x00413000
PDE: 0x027 Present, Writable, User, Execute Enabled
PTE: 0x800000002 Non-present, Writable, Supervisor, Execute Disable
Current thread ID = 0x004021c0
eax: 0x00001398, ebx: 0x00400033, ecx: 0x00000ffc, edx: 0x00409000
esi: 0x00407000, edi: 0x00409fe8, ebp: 0x00409fe4, esp: 0x00409fd0
eflags: 0x00000246 cs: 0x002b
call trace:
eip: 0x0000253f
Fatal fault in thread 0x004021c0! Aborting.

The memory address 0x00413000 points to __stack_chk_guard:

(gdb) x/fx 0x00413000
0x413000 <__stack_chk_guard>:	0x589a24a0